Analysis of polyamides has been an area of technical study since the invention of this important class of compounds. A multitude of analytical methods have been developed to study various characteristics in the product polyamides and have also been used at various stages of polyamide manufacturing processes. See, for example, Volume 17 of the "Encyclopedia of Industrial Chemical Analysis" published by John Wiley & Sons (1973). These earlier methods are applicable to the analysis of nylon polyamide product or to various stages of nylon polyamide processes. When applied to process-related measurements, the methods suffer from the fact that a discrete sample of the in process material must be taken and analyzed. This sampling and analysis can be a cause of inaccuracy and irreproducibility because of the nature of the nylon polymerization reaction, i.e., the reaction continues at a rate determined by the temperature of the material and the atmosphere surrounding the material. The invention of the present application, when applied to process related materials, avoids these problems because the analysis requires the taking of no samples, e.g., from a continuous process. This aspect of the invention at hand is an in-line analytical method.
U.S. Pat. No. 5,155,184 discloses a process for the manufacture of a polymer, the process being controlled by periodically sampling the polymer produced and analyzing the sample by near-infrared spectrophotometry. The polymer produced is a polyolefin, more specifically, polyethylene.
U.S. Pat. No. 5,339,255 describes a process for measuring an infrared spectral absorption of a reaction intermediate product of polycondensation reaction and mentions applicability to polyamide.